The invention relates to an actuator device for producing a linear movement and to a method for setting a position of a linearly movable element.
For certain adjustment tasks, there is a need for actuators by which linear adjustments that are as precise as possible can be performed. Ideally, such actuators are as small as possible, operated electrically, resistant to environmental conditions, especially contamination, and as wear resistant as possible.
It is known that such adjustment tasks can be performed manually with some effort and that electromagnetic linear actuators, spindle drives or pneumatic/hydraulic actuators can be provided. The use of piezoelectric or magnetoresistive actuators is also known. For relatively large deflections, piezoelectric actuators which operate on the caterpillar or inchworm principle are also known. For this purpose, three actuators are generally required, namely a clamping actuator element at the front and rear and an actuator element for forward motion.
Known actuators are generally complex and are not resistant to contamination and wear.
In addition to the actuator types described above, the related art also includes a linear drive which manages with just a mass, a clamping device and a single actuator element. A piezoelectric actuator is positioned between the mass and the clamping device and is supplied with a rising voltage in such a way that the deflection force resulting therefrom accelerates the mass but the force remains below the static friction force of the clamping device on which the actuator is supported. When the maximum deflection of the piezoelectric element is reached, the control voltage is reduced so quickly that the resulting contraction of the piezoelectric element leads to a negative acceleration force which, although it reduces the movement of the mass, is so great that the static friction of the clamping device is exceeded and therefore the clamping device is taken along in the direction of movement and, in the next deflection phase, forms the new point of support, now displaced in the direction of movement. If the sequence is reversed instead of the control profile comprising “slow deflection, rapid contraction”, the direction of movement of said linear motor is also reversed.
One disadvantage of this method is the dependence of the deflection on the magnitude of the current static friction of the clamping element. Particularly if the static friction changes due to the ingress of oil or dirt, the desired precision or indeed the entire functioning ability of the adjusting device may be lost. Moreover, as with all mechanical systems in which two surfaces rub against one another, the system is prone to wear over the long term and hence to changes in system properties.
JP 2000 314402 A discloses an actuator device for producing a linear movement, having a hydraulic actuator, which comprises a first piston element for actuating the actuator and a second piston element for producing the linear movement, which piston elements are assigned respective fluidically coupled working chambers, the volumes of which can be changed by movement of the respective piston element. In this case, a piezoelectric actuator is provided for exerting a force on the first piston element. Moreover, the respective working chambers are connected by two oppositely oriented check valves. JP 2001 012402 A discloses an actuator device having two piston elements, which are assigned respective fluidically coupled working chambers. A respective volume of the working chambers can be changed by movement of the respective piston element. A magnet element for exerting a force on one of the piston elements is furthermore provided.
DE 10 2008 046 562 A1 discloses a hydraulic linear drive having a piston, which is mounted slidably in a cylinder, wherein the cylinder has an inlet, via which a fluid can be introduced into the cylinder by a pumping device. The cylinder furthermore has an outlet, via which fluid can be removed from the cylinder. Provision is made here for a piezoelectric and/or magnetostrictive actuator to be provided to drive the pumping device.
An actuator having an electrostrictive body can be taken as known from JP S62 28507 A. A rod can be moved by the electrostrictive body.
Finally, EP 1 190 829 A2 discloses an actuator device for producing a linear movement, having a piston which is arranged in a cylinder. The piston can be moved by subjecting the piston to a pressure by a working fluid. Here, the working fluid is put under pressure by a driving force of a piezoelectric element in order to drive the piston.